Do not (re)start "apt-daily.system"

This unit runs unattended-upgrades. If apt itself is part of the
upgrade a restart of the unit will kill unattended-upgrades. This
will lead to an inconsistent dpkg status.

Closes: #841763
Thanks: Alexandre Detiste

debian/rules

@@ -29,6 +29,11 @@ override_dh_gencontrol:
 override_dh_installcron:
 	dh_installcron --name=apt-compat
 
+override_dh_systemd_start:
+	# Do not restart "apt-daily.service" because this script runs
+	# unattended-upgrades. So if apt itself is upgraded as part of
+	# an unattended-upgrades run it would kill itself
+	dh_systemd_start apt-daily.timer
 
 override_dh_auto_configure-arch: flags=-DWITH_DOC=OFF
 override_dh_auto_configure-indep: flags=-DWITH_DOC=ON